This application claims the benefit of Korean Patent Application No. 2001-16011 filed on Mar. 27, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical disc player, and more particularly, to an apparatus controlling a mirror signal to be constantly output independently of variations of the quantity of light from a laser beam received by a pickup or the reflectivity of a disc, and a method thereof.
2. Description of the Related Art
Recorded information has been generally reproduced by means of a magnetic system or light. When using a magnetic system, an array of the polarity of a magnetic object applied to a magnetic medium is detected to reproduce information corresponding to the polarity (or phase). This method has an advantage in that it is easy to record and reproduce information because the array of the polarity of the magnetic object is used.
On the other hand, when using light, information is reproduced by scanning light on a recording surface of a disc and detecting irregular reflections caused by pits recorded on the disc. This method has an advantage in that information retaining efficiency is excellent because a pit is recorded on a recording medium.
When reproducing information by light, CD-ROMs and DVD-ROMs have been widely used for a storage medium. A general optical disc contains several sectors, which are sectioned in a radial pattern on a circular storage medium, and several tracks, which are equally divided in a concentric circle pattern. An optical disc usually rotates at a speed of 720 RPM and is played back in the form of a concentric circle from its center to its outer diameter by an optical disc player.
The above-described optical disc player includes an apparatus generating a mirror signal capable of correctly irradiating a beam in a pickup on a target point when a track of an optical disc is jumped, as shown in FIG. 1.
Referring to FIG. 1, a conventional apparatus that generates a mirror signal is composed of an ABCD summer 10, a first peak/bottom holder 11, a low pass filter (LPF) 12, a second peak/bottom holder 13 and a comparator 14.
As shown in FIGS. 3A and 3B, a tracking error signal and a mirror signal are output when a track of a disc is jumped. At that time, the mirror signal has a 90xc2x0 phase difference with respect to the tracking error signal by which it is determined whether the mirror signal is stably incident on a target point by monitoring the mirror signal when a track of a disc is jumped.
Signals picked up by a photo diode, which is divided into four sections (not shown), are combined in the ABCD summer 10. A signal generated by the radio frequency (RF) ABCD summer 10 is received by the first peak/bottom holder 11 and is divided into two signals, a peak hold RF signal and a bottom hold RF signal, in the first peak/bottom holder 11. Thereafter, a difference between the divided two signals is calculated through the first peak/bottom holder 11. The calculated difference is low-pass filtered in the LPF 12 and, as a result, a radio frequency ripple (RFRP) signal is output. The second peak/bottom holder 13 receives the RFRP signal from the LPF 12 and outputs a center voltage of two signals passing through the peak holder and bottom holder, i.e., a radio frequency center (RFCT) signal. The comparator 14 compares the RFRP signal with the RFCT signal and outputs a final mirror signal. To output the final mirror signal, the comparator 14 receives a mirror-offset signal from an exterior source (not shown).
In the past, the mirror offset signal was fixedly used, and therefore, as shown in FIGS. 3C and 3D, a mirror signal was irregularly output depending on changes in the ABCD summer 10 according to variations of the quantity of light of laser received by a pickup and the reflectivity of a disc. That is, due to an irregular output of the mirror signal, it is difficult to determine whether the mirror signal is correctly incident on a target point when a track of a disc is jumped. Further, a mirror offset signal output depends on the type of disc, and therefore, it must be newly set up for each disc.
Accordingly, it is an object of the present invention to provide an apparatus controlling a mirror signal to be constantly output independently of variations of the quantity of light in a laser beam received by a pickup or the reflectivity of a disc.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing objects of the present invention are achieved by providing an apparatus controlling a mirror signal, including an envelope detector detecting an envelope of a signal which is reflected from an optical disc, a center voltage outputting unit outputting a center voltage of the envelope, a comparator outputting the optimum mirror signal by comparing the envelope with the center voltage using a predetermined mirror controlling signal, and a mirror signal controller outputting a predetermined mirror controlling signal to the comparator until the mirror signal output from the comparator reaches a predetermined level compared to a fixed mirror signal.
The above objects of the present invention may also be achieved by providing the mirror signal controller comprising an integrator integrating the mirror signal output from the comparator below a predetermined frequency band and a calculator checking a level of the integrated signal, continuously calculating the mirror controlling signal until the integrated signal reaches a predetermined level and outputting the calculated result to the comparator.